South Korea's president declared a period of national mourning on Sunday
At least 151 people were killed and another 150 injured during a stampede when Halloween partygoers crammed into a narrow alleyway in Seoul, South Korean officials said.
Choi Seong-beom, the chief of the Yongsan fire department, said the death toll could rise further following the incident in the leisure district of Itaewon in Seoul on Saturday night.
He added that many of the victims appeared to be young women in their twenties. Nineteen foreigners were among the dead.
South Korea's President Yoon Suk-yeol declared a period of national mourning on Sunday, saying the government would pay for the medical care of those injured and the funerals of those who died. The national mourning period will last until November 5.
Mr Yoon said the government would "thoroughly investigate the cause of the incident and make fundamental improvements to ensure the same accident does not occur again in the future."
"In the centre of Seoul, a tragedy and disaster occurred that should not have happened," he said in a national address.
"My heart is heavy and it is difficult to contain my sorrow."
Seoul authorities said they had also received 355 reports on missing people by early Sunday.
Mr Choi said more than 400 emergency workers from around the nation, including nearly all available in Seoul, were deployed to treat the injured.
Video on social media showed first responders performing CPR on people lying scattered in the street amid heavy police presence.
In one section, paramedics were seen checking the status of around a dozen people lying motionless under blue blankets.
Local media said around 100,000 people had flocked to Itaewon's streets for the Halloween festivities, which were the biggest since the start of the Covid pandemic.
Riley, a visitor from New Zealand, told the Telegraph: "I arrived early about 7.30. We’d been to a few bars. We went to the subway to pick up a friend and saw the first bodies being taken to the ambulance around 11.30.
"We guessed there was a trampling with the number of people here. I was quite afraid. Earlier in the evening, there was no space between anyone, it was really crowded."
Some local media outlets reported that the crush occured after a large number of people rushed to an Itaewon bar after hearing that an unidentified celebrity had visited.
Yoon Suk Yeol, the South Korean president, called for officials to ensure the swift treatment of the injured and review the safety of the Halloween festivites.
He also instructed the health ministry to swiftly deploy disaster medical assistance teams and secure beds in nearby hospitals to treat the injured.
As the disaster unfolded, many people were unaware of the tragedy taking place just metres away from them.
Kim, a French student, said she had arrived at a packed Itaewon tube station at about 11pm when the crowd was already struggling to exit the stairwells.
When she got to street level, the police were standing on ambulance roofs shouting at the crowd to clear and trying to reach casualties.
Her friend Jette said they had been in a bar when someone said there were casualties outside.
"We saw the ambulances and thought it was just drunk people, but then realised people were doing CPR," she said.
"The ambulances were trying to get through but they couldn’t move because there were so many people.
"I didn’t know what was happening. At first it took them 10-15 minutes to get to people."
Kim added: "It was bad. We saw people being carried past with footprint marks on their limbs. They had lost clothes."
Jette added: "I think everyone wanted to go out this year because Covid was over and they were overcompensating and there were too many people."
Meanwhile, Kerry, from the US, said she had barely escaped the crush in the narrow alleyways.
"I was struggling to breathe. Everyone around me was taller and I was very frightened. Somehow I managed to get out," she said.